The present invention relates to a toner separation and recovery apparatus for enabling recycling of toner in an electrostatic copying machine or similar electrostatographic apparatus.
In such an apparatus an electrostatic image is formed on a photoconductive drum which constitutes a dielectric member in the absence of light. Alternatively, the electrostatic image may be formed directly on a non-photoconductive dielectric member through electrostatic discharge. Toner is applied to the drum or other member to produce a toner image which is transferred and fixed to a copy sheet to provide a permanent reproduction of an original document.
Since the transfer efficiency is not perfect, a certain amount of toner in the form of a residual toner image remains on the drum after the transfer operation. This must be removed from the drum prior to the formation of a new electrostatic image to prevent the formation of a double image. It is desirable from the standpoint of conservation and economy to recycle the toner removed from the drum back to the developing unit. However, various problems such as the formation of incomplete or abnormal toner images, scattering of toner particles in the apparatus and contamination of white background areas in the copies result from the fact that the recycled toner is mixed with foreign matter and toner which was charged to a polarity opposite to the desired polarity. If, for example, the electrostatic image has a negative polarity, the toner should have a positive charge so as to be attracted to the electrostatic image. If the toner is positively charged, it will be repelled by the electrostatic image and result in an incomplete toner image.